Pregnant T. rex could aid in dino sex-typing
|Pregnant T.rex [Credit: Mark Hallett]|
In 2005, Mary Schweitzer, an NC State paleontologist with a joint appointment at the NC Museum of Natural Sciences and lead author of a paper describing the research, found what she believed to be medullary bone in the femur of a 68 million year old T. rex fossil (MOR 1125).
"All the evidence we had at the time pointed to this tissue being medullary bone," Schweitzer says, "but there are some bone diseases that occur in birds, like osteopetrosis, that can mimic the appearance of medullary bone under the microscope. So to be sure we needed to do chemical analysis of the tissue."
|A cross section of the T. rex's bone showing the medullary bone in the middle|
[Credit: Schweitzer M.H. et al. Scientific Reports]
"This analysis allows us to determine the gender of this fossil, and gives us a window into the evolution of egg laying in modern birds," Schweitzer says, although she adds that the fleeting nature of medullary bone means that finding more of it in the fossil record may be difficult.
The femur of MOR1125 was already broken when Schweitzer got it, and she acknowledges that most paleontologists wouldn't want to cut open or demineralize their fossils in order to search for rare medullary bone. However, co-author Lindsay Zanno, an NC State paleontologist with a joint appointment at the NC Museum of Natural Sciences, showed that CT scans of fossils may help narrow down the search.
"It's a dirty secret, but we know next to nothing about sex-linked traits in extinct dinosaurs. Dinosaurs weren't shy about sexual signaling, all those bells and whistles, horns, crests, and frills, and yet we just haven't had a reliable way to tell males from females," Zanno says. "Just being able to identify a dinosaur definitively as a female opens up a whole new world of possibilities. Now that we can show pregnant dinosaurs have a chemical fingerprint, we need a concerted effort to find more."
The research appears in Scientific Reports.
Source: North Carolina State University [March 15, 2016]